Early hunting, farming homogenized mammal communities of North America

According to recent study performed by the University of Nebraska-Lincoln and the Canadian Museum of Nature, people have been homogenizing the mammal populations of North America for more than 10,000 years, whether by the spear or the plow.

8.831 fossils from 365 mammal species from 366 locations in North America were analyzed by Kate Lyons of Nebraska, Danielle Fraser of the CMN, and international collaborators. The team's analysis of homogenization—the degree to which a particular mammal species in one ecological community mirrored the species composition of its neighboring communities—was made possible by relying on these ancient data.

One of the main causes of the homogeneity and heterogenization that they discovered was climate, according to a few other studies that looked at North American animals from tens of millions to millions of years ago. Other study has documented the recent human effects of land conversion, poaching, and territorial expansion, concentrating just on the last century to the previous few decades.

However, no team has examined the phenomena before and after the appearance of Homo sapiens in order to establish a baseline of homogeneity or the real scale of our contributions to it. Fraser, Lyons, and their colleagues then focused on the previous 30,000 years, a time period that includes Homo sapiens' absence from the continent, their movement throughout it, and their transition from hunting-and-gathering to intense agriculture.

The research team concluded that Homo sapiens are most likely to blame for the unparalleled rates and degrees of homogeneity seen in North American animal populations. By intensifying the resemblance between many of species, we have flattened their distinguishing character.

Lyons, an associate professor of biological sciences at Nebraska, stated, "Our conclusion is that this does have to do with early human activities and the entrance of people into the Americas."

According to the study, North American mammal populations now are more homogeneous than they were around 10,000 years ago, and by the end of the 21st century, they may be nearly four times more homogenous. According to the researchers, this change is analogous to the existing disparity in homogeneity between the rather homogenous mammal groups of the Arctic and the subtropics of central Mexico.

The pattern started sooner and was more obvious in animals weighing at least 1 kilogram (2.2 pounds), or 2.2 pounds. Moreover telling? Around 12,000 years ago, when people were exterminating mammoths, saber-toothed cats, dire wolves, and other large creatures, homogenization started to pick up speed.

These data show that homogeneity was a result of the mass extinction of big mammals, according to Lyons. She claimed that the loss of huge creatures particular to each community would have accentuated the similarities between them. And a 2019 research by Lyons and coworkers shown that those extinctions also encouraged smaller species to widen their global ranges in order to fill the geographic gaps left by their bigger counterparts. According to Lyons, expansion would have resulted in increasing territorial overlap, further homogenizing communities.

But during the previous 5,000 years, homogeneity in North America has sped even further. During this time, the human population has increased up to tenfold, and extensive farming has emerged, notably in what would become the central and eastern United States.

In comparison to other continents, North America experienced it considerably later, according to Lyons. But that's basically when people in North America transitioned from being mostly nomadic hunters and gatherers to being more sedentary and reliant on agriculture.

Coyotes, raccoons, rats, and other rodent species were drawn to the numerous human settlements that sprung up across the continent. These mammals now flourish on the waste products of these settlements and take pleasure in the extermination of predators by the people who live there.

The number of plant species in a particular habitat decreased due to the conversion of grasslands and woodlands for agriculture from hundreds or thousands to only dozens or fewer, reducing the area that pickier herbivores and the predators or omnivores that prey on them could live in. According to Lyons, cultivated fields, roads, and other man-made borders would have also served as "barriers to dispersion" that confined some species to restricted areas.

Even while there are still a few groups where narrow-ranging species exist, Lyons noted that their overall contribution to the disparity across communities has likely decreased.

What potential impact may the weather have? Between 10,000 and 500 years ago, the scientists only came across flimsy evidence. A warmer North America caused the glaciers that had covered much of present-day Canada and much of the northern United States to recede between 20,000 and 15,000 years ago. More gradual north-south temperature and precipitation gradients often result from warmer regions. According to Lyons, the uniformity of the environment brought on by global warming also tends to produce homogeneity in animal societies.

The scientists would have anticipated that the homogeneity of mammal communities would have accelerated before 10,000 years ago if climate had played a role in it. She said that since it didn't, climate was probably not a major factor.

The climatic patterns show that all of that occurred very early on, before we noticed this huge homogeneity, according to Lyons.

The researchers came to the conclusion that homogeneity has only accelerated in the last 500 years despite its pace and severity throughout the previous 5,000 years. That homogeneity might be dangerous for ecosystems if it results from the ongoing loss of keystone species whose traits and skills are particularly important, according to Lyons.

A lot of what we're seeing, she continued, "is that when we lose species, especially when we lose large species that tend to be what we call ecosystem engineers, there is a tremendous shift in the environment that is left." "Large animals engage in a variety of activities in ecosystems.

Elephants transfer nutrients throughout ecosystems a lot because they eat a lot, move around a lot, and excrete a lot. The conclusion we've reached is that ecosystems lose nutrients when they're not present.

According to Lyons, homogenized mammal groups may have less strategies for dealing with the ongoing problems of climate change and increased human intrusion since there are fewer keystone species in them.

Communities would likely be less resistant to upcoming disturbances and potential extinctions, she said. Additionally, because there is less wonderful variety, the world becomes less intriguing.

Source: University of Nebraska-Lincoln